The invention relates to a measuring arrangement for continuously measuring undulatory irregularities, more particularly rail corrugations, in the running surface of a rail of a track, comprising a measuring trolley having flanged wheels which are able to roll on the track and a trolley frame, and a distance detector arranged on the trolley frame for the contactless measurement of the distance from the rail, and also comprising a device for recording, processing and issuing the measurement signals.
For reasons which are partially still unresearched, corrugations and longer undulations may appear on railway rails laid in tracks as a result of wear. By corrugations are generally meant short-wave periodic irregularities of the running surface of a rail with amplitudes of up to about 0.4 mm and wavelengths of up to about 100 mm (this maximum length can also be up to 500 mm--depending on how it is viewed). Since these deformations become worse with the passage of time and cause progressively increasing damage to the permanent way and to rolling stock, it is important to carry out regular measurements in order to determine the most economically efficient time to eliminate the corrugations, e.g. by rail grinding.
A measuring arrangement for measuring rail corrugations and also longer undulations in the surface of a rail is already known--according to U.S. Pat. No. 4,288,855, in which a measuring trolley provided with flanged wheels is pulled by a railway vehicle along the railway at a given speed. Arranged above a rail on the frame of the measuring trolley or spaced apart from one another in the longitudinal direction of the rail are two (or in another form of construction, three) distance detectors designed as contactless electronic pickups and operating on the eddy-current principle. The amplitudes of the corrugations or undulations within a specific wavelength range may be measured by means of these detectors. The distance apart of the detectors or pickups is in this case smaller than the shortest wavelength occurring within this selected wavelength range. The pickups are connected to a measurement circuit which with the aid of a comparator forms the difference of the two measured distances and at the same time determines the average actual length of the detected wave. From these data--taking into account a transfer coefficient which is a function of the ratio of the distance between pickups to the wavelength--the amplitude of the rail deformation can be determined as an actual value. Because the distance detectors are attached to the trolley frame, the said trolley frame acts as a reference base to which the measured distances from the rail are related. Since this reference base is itself directly supported on the track, however, its position relative to the track is influenced and altered by track faults which are present--or even by the corrugations and undulations themselves--by which the measurement results are adulterated to a certain extent and cannot count as absolute values. It is true that the measurement errors can be reduced by lengthening the measuring base, but they can never be eliminated completely.
A further measuring arrangement--known from Austrian Patent Specification 390 626--has a frame which rests on the track to be measured by way of rollers arranged at the ends thereof and which serves as the measuring base. Disposed in the center of this measuring base are two angle sensors, one of which measures the angle at which the frame is inclined in an inertial coordinate system. The second angle sensor determines the angle at which a surface element of the rail to be measured is inclined in relation to the frame. This second angle sensor may be designed as a scanning element or even--if the rail surface is sufficiently reflective--operate contactlessly on the principle of an autocollimation optical system. In this, a light beam is directed at the rail and its reflection is reproduced on a detector, e.g. a position-sensitive photodiode. An evaluating circuit adds the output signals of the angle sensors and integrates them over the distance covered by the arrangement. The value obtained in this way corresponds to the profile curve averaged over the length of the measured surface element. The measurement accuracy with this measuring arrangement is equally adversely affected by any irregularities of the rail in the area of the contact points of the rollers.
Disclosed in U.S. Pat. No. 4,922,752 is an arrangement for measuring or recording the irregularities of a road surface. A four-wheeled, elongated vehicle has a sensor attached to its underside in its central region, the said sensor consisting of a laser transmitter directed at the road surface and a CCD receiver. An encoder associated with one of the wheels measures the distance covered. The data obtained are recorded by means of a recorder provided on the vehicle. In this case too, the attachment of the sensor directly to the vehicle frame has an unfavorable effect, as interfering natural frequencies of the vehicle may adversely affect the measurement accuracy of the arrangement.
The object of the present invention lies in developing a measuring arrangement for rail corrugations which produces measurement results which are more accurate and more reliable and which are simpler to process.